1. Field of the Invention
The present invention relates to a convey control device for a long object, such as a treatment agent applying device used in an inkjet recording system.
2. Description of the Related Art
Recording of images by an inkjet recording method is characterized by features of low noise, low running cost, and the ease of producing color images, and is thus rapidly becoming widely used in recent years. However, when an image is recorded on a recording medium other than exclusive paper, there are problems in the initial quality in terms of blurring, density, color tone, and show-through. Additionally, there are problems relevant to the durability of images such as water resistance and weather resistance. Therefore, proposals have been made to solve these problems.
One method of solving these problems is to improve the image quality by applying a treatment agent having a function of condensing the ink before the ink droplets land on a sheet that is a recording medium.
For example, Patent Document 1 discloses the following. In a recording medium conveying path in a treatment agent applying device, an upstream side conveying unit and a downstream side conveying unit are provided on a conveying direction upstream side and a conveying direction downstream side, respectively. A tension applying unit for applying tension to the recording medium is provided between the upstream side conveying unit and the downstream side conveying unit. According to the changes in the tension applied by the tension applying unit, the conveying speed of the recording medium is controlled.
An example of convey control of a long recording medium with the tension applying unit is described with reference to FIG. 2. FIG. 2 is a schematic diagram of a treatment agent applying device. Detailed configurations and functions of this treatment agent applying device are described in the detailed description of the preferred embodiments.
A treatment agent applying device 101 includes multiple in-feed rollers 1, which are rotatably supported, and which include bearings (not shown) provided at edge parts of the rollers. Accordingly, a conveying path for a recording medium W is secured. A feed-in roller that is rotated by a motor (not shown) is denoted by a reference numeral 2, and a feed-in nip roller 4 is pressed against the feed-in roller 2 via the recording medium W. The recording medium W that is sent out by the feed-in roller 2 and the feed-in nip roller 4 is slightly loosened to form an air loop part AL.
On the conveying direction upstream side of the recording medium W, there is provided an upstream side conveying unit constituted by an in-feed roller 8 rotated by a motor (not shown) and a nip roller 9. On the conveying direction downstream side of the upstream side conveying unit, there is provided a downstream side conveying unit constituted by an out-feed roller 14 rotated by a motor (not shown) and a nip roller 9.
Between the upstream side conveying unit and the downstream side conveying unit, there is provided a first dancer unit 17. On the conveying direction downstream side of the downstream side conveying unit, there is provided a second dancer unit 18. As a brake (hereinafter, “electromagnetic brake X”) for holding the first dancer unit 17 and the second dancer unit 18 at a predetermined position is turned OFF, and the first dancer unit 17 hangs down by the recording medium W, when printing starts, tension is applied to the recording medium W passing through applying units 13f, 13r for applying a treatment agent having a function of condensing the ink.
Furthermore, as the electromagnetic brake X for holding the second dancer unit 18 at a predetermined position is turned OFF, and the second dancer unit 18 hangs down by the recording medium W, when printing starts, tension is applied to the recording medium W positioned between the out-feed roller 14 and an inkjet printer. This configuration cancels out the loosening of the recording medium W caused by a speed difference between the treatment agent applying device 101 and the inkjet printer (not shown) provided on the conveying direction downstream side of the of the treatment agent applying device 101.
The treatment agent applying device 101 implements the above tension control at the time of printing. Tension is applied to the recording medium W by the first dancer unit 17 and the second dancer unit 18 based on a print preparation instruction catalyst signal sent from the inkjet printer before printing starts.
In a state where the electromagnetic brake X is turned off and the first dancer unit 17 and the second dancer unit 18 are hanging down by the recording medium W, in a case where the in-feed roller 8 and the nip roller 9 or the out-feed roller 14 and the nip roller 9 have a small holding force, for example, when the first dancer unit 17 draws in, by gravity, the recording medium W from the air loop part AL, and draws in the recording medium W between the out-feed roller 14 and the inkjet printer, the first dancer unit 17 may fall down from the predetermined position.
In order to prevent this, in a state where a brake (hereinafter, “electromagnetic brake Y”) for preventing the rollers from rotating is turned on, the in-feed roller 8 and the out-feed roller 14 are in a standby state from when a print preparation instruction catalyst is given to when conveying of the recording medium W starts. When the recording medium W starts to be conveyed, the electromagnetic brake Y is turned off based on a reception catalyst signal of a conveying start instruction from the inkjet printer, so that the in-feed roller 8 and the out-feed roller 14 can be driven.
Then, according to drive signals equal to the conveying speed, which are output to the treatment agent applying device 101 from the inkjet printer, the motors (driving sources) of the feed-in roller 2, the in-feed roller 8, and the out-feed roller 14 are driven, so that the recording medium W starts being conveyed.
Subsequently, the loosening amount of the recording medium W is detected by air loop amount detecting units 19g, 19h, 19i and the driving source of the feed-in roller 2 is controlled, the height position of the first dancer unit 17 is detected by position detecting units 19a, 19b, 19c and the driving source of the in-feed roller 8 is controlled, and the height position of the second dancer unit 18 is detected by position detecting units 19d, 19e, 19f and the driving source of the out-feed roller 14 is controlled.
Furthermore, when stopping the printing, the driving sources of the feed-in roller 2, the in-feed roller 8, and the out-feed roller 14 are stopped based on a reception catalyst signal of a conveying stop instruction from the inkjet printer, and the electromagnetic brake Y is turned on to stop the conveying operation.
That is to say, during a regular stop state, the electromagnetic brake X is turned on and the electromagnetic brake Y is turned off. While applying a tension before printing, the electromagnetic brake X is turned off and the electromagnetic brake Y is turned on. During printing, the electromagnetic brake X is turned off and the electromagnetic brake Y is turned off. By the aforementioned control operations, a predetermined tension is applied to the recording medium W.
As described above, in a state where the electromagnetic brake X of the first dancer unit 17 and the second dancer unit 18 is turned off and the electromagnetic brake Y of the in-feed roller 8 and the out-feed roller 14 is turned on based on a print preparation instruction catalyst signal from the inkjet printer, and the first dancer unit 17 and the second dancer unit 18 hung down and tension is applied to the recording medium W, the treatment agent applying device 101 is in a standby state until conveying is started.
In a case where the electromagnetic brake Y of the in-feed roller 8 and the out-feed roller 14 is turned off to start conveying the recording medium W according to a reception catalyst signal of a conveying start instruction from the inkjet printer, and the driving source of the in-feed roller 8 and the out-feed roller 14 has a property of not having a conveying force unless driving signals greater than a predetermined speed are input, or in a case where there is a time lag until an output start catalyst of the drive signal based on a reception catalyst signal of a conveying start instruction, the in-feed roller 8 and the out-feed roller 14 do not have a conveying force until the in-feed roller 8 and the out-feed roller 14 start to have a conveying force, which means there is a time period during which the in-feed roller 8 and the out-feed roller 14 cannot rotate by themselves.
During this time period, the hanging down first dancer unit 17 or the second dancer unit 18 draws in, by gravity, the recording medium W from the downstream side or the upstream side in the conveying direction. Accordingly, the first dancer unit 17 or the second dancer unit 18 falls down to a lower limit position from a predetermined control position. Thus, tension cannot be applied to the recording medium W.
Furthermore, when stopping printing and decelerating, there is a case where the in-feed roller 8 and the out-feed roller 14 have a property of losing a conveying force when the driving source of the in-feed roller 8 and the out-feed roller 14, which is driven by the drive signals sent from the inkjet printer, becomes slower than a predetermined speed, and a case where there is a time lag from an output stop catalyst of the drive signal sent from the inkjet printer until a conveying stop instruction.
In this case also, until the electromagnetic brake Y of the in-feed roller 8 and the out-feed roller 14 is turned on according to a conveying stop instruction, the in-feed roller 8 and the out-feed roller 14 do not have a conveying force and cannot rotate by themselves, and the hanging down first dancer unit 17 or the second dancer unit 18 draws in, by gravity, the recording medium W from the downstream side or the upstream side in the conveying direction. Accordingly, the first dancer unit 17 or the second dancer unit 18 falls down to a lower limit position from a predetermined control position. Thus, tension cannot be applied to the recording medium W when starting the next conveying operation.
FIG. 10 illustrates a state where the first dancer unit 17 or the second dancer unit 18 has fallen to a lower limit position from a predetermined control position by gravity according to the above described phenomenon.    Patent Document 1: Japanese Laid-Open Patent Publication No. 2004-189449